PORTLAND, Ore. (AP) -- Motorists in the Portland area will soon become familiar with the faces of long-forgotten homicide victims. The photographs of Cecilio Corrales, Gary Hanberg, Eunice Karr and other people killed many years ago will be placed on billboards around Multnomah County as part of an advertising campaign by the sheriff's cold-case team. The campaign, built around the theme of "Know something? Say something," urges people to come forward if they know anything about the roughly three dozen unsolved homicides under review by cold-case detectives. The billboards -- there will be a dozen in all -- provide a tip line to call and a Web site where people can find more details about the unsolved slayings. "The passage of time provides people familiar with the case another chance to reconsider their level of cooperation in working with our detectives, to put to rest a tragic death ..." said Capt. Monte Reiser, head of the sheriff's investigations division. The sheriff's office formed its cold case unit about a year ago, drawing on eight retired detectives who volunteer their time to solve cases dating back almost 50 years. In at least eight of 13 cases that have been deemed a priority for the cold-case team, forensic evidence has been submitted to the Oregon State Police's crime lab, using new technology including DNA evaluation. "People familiar with a cold homicide case in any way, who have knowledge that may seem obscure or irrelevant, are encouraged to contact our cold-case detectives," Reiser said. "There's no way in knowing if the formation they share may be what detectives have been looking for to help close the case." Space for the billboards has been donated by Clear Channel Outdoor; another $2,300 to produce the billboards was donated by the Multnomah County Sheriff's Management Association, the Deputy Sheriff's Association, the Corrections Deputy Associations and the retired detectives. Officials said most of the vinyl billboards will be in east Portland and Gresham, some close to where the slayings took place.